This invention relates to a polyamide composition for molding that contains fibrous wollastonite, and, in greater detail, it relates to a polyamide composition for molding that has superior rigidity, strength, toughness, dimensional stability, resistance to chemicals, external surface appearance and sliding characteristics in high-humidity, high-temperature environments, which has a low coefficient of linear expansion and which is of low warpage in spite of the fact that there is one type of fibrous filling material. Furthermore, it relates to a polyamide composition of which excellent properties are maintained in recycled objects produced using spur or runner emerged from injecting the polyamide composition, but which make its color control easier.
It is well known that reinforcing materials and/or filling materials are compounded with thermoplastic polymers for molding in accordance with the properties that are required by the uses of molded products.
In general, when inorganic filling materials of which glass fibers, carbon fibers, silica, clay, talc and mica are representative are used singly or in combination, improvement can be obtained in some of the required properties of molded materials such as rigidity, toughness, surface external appearance, strength, low warpage, dimensional stability and sliding characteristics and in the coefficient of linear expansion of the resin composition. On the other hand, there is a tendency for deleterious effects to be exerted on other properties. Of course, this tendency becomes marked as the content of inorganic filling material in the resin composition for molding that is finally obtained is increased. At the same time, there is also the problem that the cost of the resin composition is increased. On the other hand, in recent years, semi-aromatic polyamides that contain aromatic monomer components in a portion of their structural elements have come to be widely used because of their superior high temperature rigidity, heat resistance, resistance to chemicals and water-absorbing capacity. Attempts have also been made to apply these same polyamides and aliphatic polyamides of which nylon 6 and 66 are representative to various types of molded products as thermoplastic polymers for molding of superior mechanical strength, rigidity and heat resistance. In addition, compositions in which inorganic filling materials are compounded for the purpose of further improving rigidity and toughness are well known.
However, attempts to improve toughness and impact resistance without impairing the superior properties of the semi-aromatic polyamides by compounding inorganic filling materials with semi-aromatic polyamides have not been made to any great extent.
Under these circumstances, as an example of compounding various inorganic filling materials with semi-aromatic polyamides, there is the composition described, for example, in Japanese Patent Application Early Disclosure No. 3-210359 [1991]. A study was made of improving heat resistance due to increase of crystallinity and improving surface external appearance by compounding wollastonite or other various fillers having acicular particles which is present in natural metamorphic rock comprised essentially of calcium metasilicate with the semi-aromatic polyamide compositions as disclosed in that application. Molded objects may be colored for various uses, and polyamide composition having less effects of containing such colorant on mechanical properties and toughness is desired as injection molding compositions and spur and runner emerged from injection molding for production of molded objects are desired to be recycled to respond a social need for contribution to reduction of industrial waste in the recent years.
However, nothing has been disclosed concerning the length, diameter and aspect ratio of the wollastonite and aromatic polyamide compositions of superior rigidity, strength, toughness, dimensional stability, resistance to chemicals, external surface appearance sliding characteristics and warping characteristics in high-humidity, high-temperature environments and having low coefficients of linear expansion have not been provided.
It is an object of this invention is to provide a polyamide composition for molding of superior rigidity, strength, toughness, dimensional stability, resistance to chemicals, external surface appearance and sliding characteristics in high-humidity, high-temperature environments, of which the resin composition has a low coefficient of linear expansion and which is of low warpage in spite of the fact that there is one type of fibrous filling material.
Another object of this invention is to provide a polyamide composition of which excellent properties are maintained in recycled objects produced using spur or runner emerged from injecting the polyamide composition and molded objects even if they are colored by injecting colored molding composition. We have found that the abovementioned objects are achieved by a polyamide composition containing wollastonite having a specified diameter, length and aspect ratio. The molding polyamide composition according to the present invention shows superior rigidity, strength, toughness, dimensional stability, resistance to chemicals, external surface appearance and sliding characteristics in high-humidity, high-temperature environments, having a low coefficient of linear expansion and of low warpage. Furthermore, the molding polyamide composition according to the present invention provides advantages that excellent properties of molding polyamide composition according to the invention are maintained in recycled objects produced using spur or runner emerged from injecting the polyamide composition and molded objects even if they are colored by colorant being contained in the molding polyamide composition.
An aromatic polyamide composition for molding comprising A. 100 parts by weight of a semi-aromatic polyamide having an aromatic monomer component of greater than 20 mol % and said polyamide having at melting point greater than 280xc2x0 C. and B. 5 to 170 parts by weight of wollastonite of a number average length of approximately 5 xcexcm to approximately 180 xcexcm and a number average diameter of approximately 0.1 xcexcm to 15.00 xcexcm and the average aspect ratio of which is greater than 3:1.
Another form of this invention is directed to polyamide composition comprising A. 100 parts by weight of a semi-aromatic polyamide in which (a) the quantity of aromatic monomer in the monomer component that forms the polyamide is greater than 20 mol %, and polyamide having (b) a dicarboxylic acid component from the group consisting of terephthalic acid, a mixture of terephthalic acid and isophthalic acid in which the quantity of terephthalic acid in the dicarboxylic acid component is greater than 40 mol %, a mixture of terephthalic acid and adipic acid and a mixture of terephthalic acid, isophthalic acid and adipic acid in which the quantity of terephthalic acid in the dicarboxylic acid component is greater than 40 mol % and, (c) a diamine component selected from the group consisting of hexamethylenediamine and a mixture of hexamethylenediamine and 2-methylpentamethylenediamine and with (d) the melting point greater than 280xc2x0 C.; and B. 5 to 170 parts by weight of wollastonite of a number average length of approximately 5 xcexcm to approximately 180 xcexcm and a number average diameter of approximately 0.1 xcexcm to 15.00 xcexcm and the average aspect ratio of which is greater than 3:1.